MCDANIEL TANK RHYOLITE
The McDaniel Tank Rhyolite obsidian source, discovered by Jeff Ferguson
(Missouri Research Reactor Center), is part of the Squaw Peak Volcanic Center,
identified and described by Bobrow (1983; see also Bobrow et al. 1983). The
Squaw Peak Center is in the far northeastern portion of the Mogollon-Datil
Volcanic Province dated between about 35 and 20 Ma (Shackley et al. 2017). The
Squaw Peak Volcanic center is comprised of three distinct mid-to-late Tertiary
(Neogene) rhyolite domes, the oldest is the flow banded phenocryst poor, high-K,
high SiO2 rhyolite tephra that covers much of the northern part of
Squaw Peak and north that includes McDaniel Tank dated by K-Ar to 18.3 ± 0.7 Ma (Bobrow 1983:15; see
image below). The tuff is characterized as a dark brown to black, welded, basal
ash flow tuff overlain, in parts, by a folded lithoidal lava. Obsidian was not
recorded by Bobrow. The marekanites
appear to be lava fragments quenched during the ash flow eruptive event. Field
survey during August of 2012 indicated outcrops of marekanite clusters at
various points in the 4.1 km3 tuff volume, although the distribution
of the ash flow seems larger than that recorded by Bobrow (Bobrow 1983:15). While the
volume is relatively low, the area covered is quite large given the relatively
thin depth of the ash flow as seen in 2012.
Analysis by XRF and NAA by Bobrow (1983) indicates a relatively close similarity between the major, minor, and trace elements between his sample of rhyolite lava and the obsidian given the expected differences between a crystalline rhyolite and glass (see Bobrow et al. 1983:215).
Table 1. Elemental concentrations for the McDaniel Tank Rhyolite obsidian source standards, mean values for Bobrow et al. (1983) rhyolite analysis, and USGS RGM-1 rhyolite standard. All measurements in parts per million (ppm). n.r.=no report
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Table 2. Mean and central tendency for the data in Table 1.
Table 3. Major and minor oxides for one sample of McDaniel Tank obsidian, Bobrow et al. (1983) analysis of a McDaniel Tank rhyolite sample, and USGS RGM-1 rhyolite standard.
|
Sample |
SiO2 |
Al2O3 |
CaO |
Fe2O3T |
K2O |
MgO |
MnO |
Na2O |
TiO2 |
|
McDaniel Tank, NM |
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|
082812-1-1 |
76.01 | 12.158 | 1.143 | 1.60 | 4.758 | 0.11 | 0.083 | 3.44 | 0.247 |
| Bobrow et al. (1983) analysis | 73.95 | 14.24 | 0.09 | 1.231 | 4.55 | 0.23 | 0.08 | 4.52 | 0.25 |
|
RGM1-S4 USGS standard |
73.73 |
13.190 |
1.3998 |
2.221 |
4.900 |
<.001 |
0.0403 |
4.01 |
0.237 |
1 FeO
Figure 1. The northeastern Mogollon-Datil Volcanic Province volcanic centers (from Bobrow 1984)
REFERENCES
Bobrow, D.J. 1984, Geochemistry and petrology of Miocene silicic lavas in the Socorro-Magdalena area of New Mexico. Master's thesis, Department of Geology, New Mexico Institute of Mining and Technology, Socorro.
Bobrow, D.J., P.R. Kyle, and G.R. Osburn, 1983, Miocene rhyolitic volcanism in the Socorro Area of New Mexico. In C.E. Chapin (Ed.) Socorro Region II, New Mexico Geological Society 34th Annual Field Conference, pp. 211-218. New Mexico Institute of Mining and Technology, Socorro.
Shackley, M.S., L.E. Morgan, and D. Pyle, 2019, Elemental, isotopic, and geochronological variability in Mogollon-Datil Volcanic Province archaeological obsidian, Southwestern New Mexico: solving issues of inter-source discrimination. Geoarchaeology 33:486-497.
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